Multivibrator and impulse generator



p 1952- P. J. WALSH 2,611,890

MULTIVIBRATOR AND IMPULSE GENERATOR Filed Feb. 21, 1949 IN V EN TOR.

Patented Sept. 23, 1952 it MULTIVIBRATOR AND IMPULSE GENERATOR Philip J Walsh, San Francisco, Calif. Application February 21, 1949, Serial No. 77,550 g Claims. (Cl. 321-438) This invention relates to a magnetic multivibrator.

It is one of the objects of my invention to provide a multivibrator and impulse generator having no moving parts. I v It is another object of my invention to provide a multivibrator and impulse generator requiring no electron emission devices.

It is still another object of my invention to provide an impulse generator which develops slow spaced current pulses of predetermined time ing and forming part of the present specification.

I shall now proceed to describe this form in detail, which illustrates the general principles of my invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of my invention is best defined by the appended claims. 1

Referring to the drawings:

The single figure is a system diagram depicting one form of my invention. p

In the drawing I show a sourceof alternating current power I connected through the variable impedance 2 to Winding 3 wound on the iron core 4; When current from source I flows through winding 3 a magnetic flux is set up in core 4 which induces electromotive forces in windings 5 and 6 causing current to flow through load 1 and surge between condenser 8 and the coils 5 and 6.

If the value of the voltage of source I is gradually increased from zero up to the full operating value, the value of the voltage applied to load I can be made to stay near zero until the full operating voltage is applied to coil 3 at which point the value of the voltage applied to load 1 jumps to its full operating value. This abrupt change occurs in the manner set forth in my application for Magnetic Trigger System, Serial No. 57,760, filed November 1, 1948. After the voltage has reached its full value across load I it can be made to drop to nearly zero value, by connecting a very small load across coil 5 or across the condenser terminals 9 and I0, or by reducing the value of the voltage applied to winding 3.

When the full operating voltage is applied to load 1, if load 1 is disconnected; the voltage across coil 5 rises to a new value'. Now when load 1 is again connected across coil 5, the voltage does not drop back to the operating value, but instead,

drops to zero value first and then builds up to the full operating value.

The explanation of the above described observed phenomena is as follows: the magnetic structure, comprising the core :3 and the coils 3,

5 and 6, is essentially a three-leg transformer, the primary being coil 3. In the absence of the load circuit 1 and the connectionwhich includes the condenser 8, the voltage across the coils 5 and 6 will be proportional'to' the number of turns in the coils times the flux through the legs of the core upon which they are wound. If all three coils have the same number of turns the sum of the voltages across coils 5 and =6 will be very nearly equal to that across coil 3, the difference from equality being accounted for by some small magnetic leakage of fiux which bypasses either of the two secondary coils. Upon open circuit, is described, the potential across coil 5 will be very materially greater than that across coil 6 because of the much lower reluctance of its shorter magnetic path and the resulting excess of flux through the center leg.

If, now, the condenser 8 is connected in the circuit as shown, the loop including coil 6 and condenser 8 will appear, at least for low primary voltages, as a reactive circuit. For low input voltages the reactance will be primarily inductive, but the impedance of the circuit as a whole will be less than that of the coil 6, since the capacitive reactance of the condenser is subtracted from the inductive reactance of the coil 6. Current will flow inthis circuit which is proportional to the diiferential voltage between coils 5 and 6 divided by the effective impedance of the circuit as a whole. This secondary current will set up a counter-flux in the center leg on which coil 5 is wound. In the coil 6 it will set up a flux in the same direction as the flux from the primary 3. The result is that the voltage across coil 5 falls while that across coil '6 rises.

With increasing primary voltage and flux the transformer leg within coil 6 approaches saturation, and the apparent inductance of this leg therefore decreases. A point is therefore quickly reached where the inductive reactance of coil 6 equals the capacitive reactance of the condenser 8. At this point the reactance of the circuit fed by the coil 5 becomes zero and the remaining impedance is only the very small resistive impedance due to the winding 6, the actual resistance of this winding being effectively in parallel with a relatively smallerrvirtual resistance due to the power losses in the core. At this point on the operational curve of the device the voltage across coil approaches zero.

The condition of zero reactance is, however, unstable. As it is approached the current through coil 6 and its series condenser increases rapidly, the efiective inductance of the coil 6 falls with increasing saturation and the impedance of the circuit as viewed from coil 5 changes sign, becoming predominantly capacitive. When this occurs the current in the circuit, which up to this point has lagged the voltage, now leads. The back E. M. F. induced in the coil 6 therefore reverses in sign and now boosts that induced in the coil 5 as far as a voltage produced across the condenser 8 is concerned. The flux induced within the coil 3 now becomes in-phase with that magnetic circuit including these two coils, so

that the flux through coil 5 is no longer the primary flux minus the flux through coil 6 but is the primary flux plus that through coil 6. Therefore the voltage across coil 5 becomes proportional to the number of turns in the coil multiplied by nearly double the primary 'fiux, the difference again being the leakage. The point .at which this sudden increase in voltage in coil 5 occurs is defined as the jump point. of a load 7, once the jump has occurred the voltage applied to the primary coil 3 may be very greatly reduced before the reverse action takes place; when it does the values of the voltages across coil5 and the condenser- 8 drop back very suddenly to a low value. This occurs, of course, when, due to the reduction of flux within the coil 6, its efiective inductance rises and the inductive drop across it again becomes equal to the capacitive drop across the condenser 8. As in the case of the jump the balanced condition is unstable.

The addition of .the load '1 across the coil 5 serves to bring the, jump and break points closer together. From the description of the mechanism of the jumps it can be seen thatif the resistance of load is sufficiently decreased it may be made to absorb enough power so that the core within coil 6 will never saturate and no jump willoccur. With a somewhat higher resistance load ful1 voltage applied acrossthe primary may be just sufficient to cause the jump,

and when this occurs a very slight increase in the load will cause the break to.occur and-the voltage across coil 5 to drop back to a low value approaching zero.

By connecting another unit, similar to the.

one described but of smaller size, across load I,

or across the terminals 9 and ID, the multiat which the jump occurs it absorbs very little power and its eiie'ctive impedance is therefore high. Connected in parallel with the load. 1

it therefore draws verylittlecurrent. When the jump does occur in the second unit it suddenly increases the load .upon the first unit beyond the.

point at which the .latter can maintain its. ea-

In the absence to swing between zero and 120 volts during a time period of about two seconds. It could be made to remain above 100 volts, or at zero value the greater portion of the time by adjusting the impedance 2. By adjusting the impedance 2 so as to raise the voltage applied to coil 3 very rapid pulsations of current through load I could be obtained. An oscilloscope connected across load '1 indicated that-these pulsations contained the fundamental frequency of source I and a large number of harmonics thereof.

These tests were made with switch I! closed pacitive loaded state; the voltage break then occurs, causing the voltage across coil 5.to drop back to its near Zero value. The drop in voltage across the second unit brings this,.too, below'the break point, re-establishing the initial condition,

aiter which the action repeats.

In an actual test of my. invention, load I was a watt, volt lamp. The needle of a voltmeter connected across the lamp could'be made 2 thus connecting coil 12 across load I. The impulsetiming can also be changed by adjusting resistor 13. Byproper design of the circuit elements load 1 can be of any kind or size and by spacing the jump and break points of the two units the proper distance apart, any kind of impulses can be obtained. It is seen that when the voltage applied to coil l2 reaches a predetermined value, the voltage across resistor l3 jumps to its highest value and the current through coil [2 increases. But this increased load across-coil 5 causes the voltage across load I todrop to zero thus momentarily shutting off bothunits, after which the first unit builds up to full voltage across load I, to be shut off again by the action of the control unit, etc. V

Impulses of very long time duration can be obtained in load! byopening switch It thus connecting resistor IS in the circuit as shown. Re.- sistor Hi can be a short length otfine nickel wire,.or made of any other material having a high temperature coefiicient. Under these conditions when thevoltage ac ross resistor 13 jumps to its full value, the valueof the current flow-.

ing throughresistor l5 increases andheats this resistor causing its resistance in ohms to increase enough to stop the energy storage-flywheel action in the circuit including the coils l! and I8, which in turn causesthe voltage across resistor I3 to dropto its lowest value. Thus the current flow through winding 12 is abruptly reduced and load current continues to flow through load I until resistor lfi cools sufliciently-to allow the control unit to jump, increase the current a through coil l2 and drop the, value ofthc voltage across load Ito zero. i

The output of the device into its load circuit comprises successionsof wave trains of the supplyfrequenoy, the envelope of which has'a substantially rectangular waveform. Because of the natureof the supply the frequency of these upo-nthe time-temperature characteristics of the. load, oscillations of the .multivibrator type will occur with purely resistive or capacitive loads v having negligibletemperature coefiicients. Even when unvaryingloafds are used and the full value of the input. voltage to the first unit is applied suddenly so'thati't might be expected'that the jump'would'occu'r'upon the'first cycle, this does nomuin general, occur,several cycles being required'ior the device to pass through its unstable state. With the two devices connected'in cascade as shown the period of oscillation is determined by the sum oi the lag times of the two units.

Since the';time rate can be set to meet any given conditions the system is very useful and it is apparent that it has many industrial applications. For example, it may be used as a power supply andtiming unit for flashing advertising,

primary coilithe'reof connected across said last mentioned secondary coil.

2. A device in accordance with claim 1 including a load connected across at least one secondary coil of said second transformer.

3. A deviceiin accordance with claim 1 including a load connected across one secondary coil of said second transformer, said load comprising a resistor having a high temperature coeiiicient of resistance so as to change in value when heated by current from said second transformer.

4. A device in accordance with claim 1 including a resistor connected in series with the condenser and secondary coils of said second transformer unit.

. 5. A device: in accordance with claim 1 ineluding a resistor having a high temperature coeflicient of'resistance connected in series with the condenser and secondary coils of said second transformer unit, said resistor having a carrying capacity such as to cause it to change in value materially when supplied with current from said secondary coils."-

i PHILIP J. WALSH.

REFERENCES CITED The following references are of record in the file of this fpatent:

UniT n STATES PATENTS Number Name Date 2,202,715 Partington May 28, 1940 2,215,893 ,Walker et al Sept. 24, 1940 2,222,048 .5 Stevens et al. Nov. 19, 1940 2,265,296 Lee Dec. 9, 1941 2,309,586 Haines Jan. 26, 1943 2,324,634 McCreary July 20, 1943 7 2,462,371 B-yEngle Feb. 22, 1949 2,463,540

Huge Mar. 8, 1949 

